During return travel to earth, ionization of molecules occurs in the upper atmosphere adjacent to an aerospace launched reentry vehicle. The electrons and ions of oxygen and nitrogen so produced form a plasma of increasing charge density. At some point during vehicle descent, the charge density of the plasma reaches a level at which a conducting sheath is formed on the casing wall of the vehicle to reflect rf signals therefrom. Heretofore, such conducting plasma sheath caused a communication 6 blackout at distances between 100,000 and 20,000 feet above the earth's surface. Accordingly, the conducting plasma sheath is regarded by persons skilled in the art as a blackout shield detrimental to aerospace vehicle flight missions.
In an attempt to solve the communication problem involving the aforementioned conducting plasma sheath at different frequencies and power levels, travel guidance control over the reentry vehicle throughout its descent was provided by signals from a plurality of stationary satellites to maintain reentry travel along a shallow glide angle path. The conducting plasma sheath formed on the reentry vehicle as a blackout shield was thereby limited to a bottom portion thereof so that communication with one of the stationary satellites could be maintained through an antenna mounted on a vertical surface portion of the reentry vehicle at its tail end.
It is therefore an important object of the present invention to provide communication with a reentry vehicle throughout its descent without restriction or confinement of the conducting plasma sheath formed thereon, and without thereby directionally limiting communication to one source of guidance control data, as heretofore proposed in order to solve the communication blackout problem.
It is a further and related object of the invention to enable radio frequency communication with a reentry vehicle directly through the conducting plasma sheath formed thereon during descent as a result of atmospheric ionization adjacent to the casing wall of the vehicle.